During the construction of a metal building, it is normal firstly to construct a framework of metal structural members, including purlins and wall girts, and then to provide this framework with heat insulation and a cladding before casting a concrete floor in the building. Consequently, the ground on which the building is being erected is often obstructed by rubble and the like. For this reason, it is preferred to apply the insulation and the cladding from the exterior of the building framework.
In the past, the insulation and cladding has normally been applied to the building framework by firstly positioning a blanket of glass fibre insulation material, provided with a vapour barrier facing, over the exterior of the roof purlins and wall girts of the building framework, and then securing the cladding at the exterior side of the glass fibre insulation material. The securing of the cladding has normally been effected by means of screws inserted, from the exterior of the building, through the cladding and the glass fibre insulation material and into threaded engagement with the purlins and girts. These screws are provided with compressive washers for sealing screw holes in the cladding, and the screws must be tightened sufficiently to compress the washers for preventing the ingress of moisture through the screw holes.
Such tightening of the screws causes compression of the glass fibre insulating material between the cladding and the purlins or girts, which substantially reduces the heat insulating properties of the glass fibre insulating materials at the compressed portions thereof, relative to the uncompressed portions.